The present invention relates to a clamping apparatus of construction molding board, which possesses excellent mechanical properties and can be easily assembled, so as to reduce the overall cost of a construction project.
As shown in FIGS. 1 and 2, a clamping apparatus 10 of the prior art comprises a base 12, a base body 14, a press bar 22, and a torsion spring 24. The base 12 and the base body 14 are integrally made. The base body 14 is U-shaped in its cross section and provided therein with a receiving space 16 and a canal 18 which is located at the rear end of the base body 14 and in communication with a round hole 13 of the base 12. In addition, the base body 14 is composed of two tongues 20 located at the front end thereof. The press bar 22 is pivotally mounted in the receiving space 16 by means of a shaft pin and is provided at the bottom edge thereof with a serrated arresting portion 21, as shown in FIG. 5. The arresting portion 21 is opposite to the canal 18. The torsion spring 24 has a body 25 pivoted to the tongues 20 by a shaft pin 26. The torsion spring 24 has one end forming a hook 27 urging the press bar 22 and another end which urges the base 12. The torsion spring 24 is used to provide the press bar 22 with an arresting force. In operation, the base 12 of the clamping apparatus 10 is placed on a construction molding board 28, as shown in FIG. 3, such that a reinforcing steel 29 passing through the molding board 28 is arranged in the round hole 13 and the canal 18 and that the reinforcing steel 29 is urged by the arresting portion 21 of the press bar 22. Similarly, another clamping apparatus 10 is used to hold another end of the reinforcing steel 29 and another molding board 28.
The clamping apparatus 10 of the prior art described above has several shortcomings, which are elucidated hereinafter.
The torsion spring 24 has one end urging the press bar 22 and another end urging the base 12. These two ends of the torsion spring 24 form a single line thrust, which often results in a greater stress and strain. As a result, the strength and the service life span of the torsion spring 24 are greatly undermined. In addition, these two ends of the torsion spring 24 are situated at the two sides of the body 25, thereby bringing about the couple of forces causing an angular displacement of these two ends at such time when the torsion spring 24 is exerted upon by a force. Such a situation can often lead to the deviation of the press bar 22 from its position.
The press bar 22 and the torsion spring 24 are respectively pivoted to the base body 14 and the tongues 20 by means of the shaft pins 23 and 26, thereby making the manufacturing process of the clamping apparatus 10 rather cumbersome and costly.
The overall material cost of the clamping apparatus is relatively high in view of the fact that the base body 14 is provided with two tongues 20 for mounting the torsion spring 24 and that two shaft pins 23 and 26 are used to fasten the press bar 22 and the torsion spring 24.
In using the clamping apparatus 10 of the prior art, one must hold securely with one hand the base 12 and pull or tug with another hand at the press bar 22 so as to fasten or unfasten the reinforcing steel 29. It is therefore difficult for a worker to use the prior art clamping apparatus 10.
As shown in FIG. 2, the clamping apparatus 10 has two depressed side walls 14a serving to keep the press bar 22 at bay so that the press bar 22 does not sway on the shaft pin 23. Therefore, the space between the press bar 22 and the base body 14 can be filled accidentally with the cement mortar. The filled cement mortar can not be easily removed manually from the space that is relatively narrow. The operation of the press bar 22 is therefore hampered.
As shown in FIG. 3 illustrating the clamping apparatus 10 in use, the molding board 28 is under a considerable pressure exerting thereon by the filled cement mortar, thereby causing the serrated arresting portion 21 of the press bar 22 to hold the reinforcing steel 29 tightly. Therefore, it is often necessary that a hammer is used to hit the press bar 22 to break up the intimate association of the serrated arresting portion 21 with the reinforcing steel 29 so as to remove the clamping apparatus 10. In addition, the action of hitting the press bar 22 with a hammer can often bring about a damage to the serrated arresting portion 21 and run the risk of hitting accidentally the hook 27. The torsion spring 24 is made of a high carbon steel material and can be therefore ruptured easily by such an accidental mishap.
As shown in FIG. 4, the torsion spring 24 is composed of a rather lengthy portion between the hook 27 and the body 25 and of an irregularly wound portion. Therefore, the torsion spring 24 is vulnerable to a mechanical fatigue and a failure to urge the press bar 22 to restore its position.
When the clamping apparatus 10 is accidentally impacted, the hook 27 of the torsion spring 24 can become detached to fall on the ground.
As shown in FIG. 5, the reinforcing steel 29 is not held securely in the canal 18 by the arresting portion 21 because the cross section of the reinforcing steel 29 is shown to be held at only two points.